Melting and Melting Point

Tishk International UniversityFaculty of ScienceMedical Analysis Department

Practical General ChemistryFor

First grade Students

Lab. 03

1- High ordered arrangement of particles.

2- Low thermal energy of particles.

3- Restricted motion of particles

4- Regular shape.

Solid Compounds Liquid Compounds

1- Low ordered arrangement of particles.

2- High thermal energy of particles.

3- free motion of particles

4- Random shape.

Melting Process

Melting is a physical process in which a solid phase

compound changed into liquid phase, without

changing the properties of the compound

Melting point: is a temperature in which the liquid and solid are in equilibrium.

All the solid compounds during the heating gave a range,known as melting range.

Pure compounds during heating process characterized bya sharp melting range (0 – 2) °C, while compoundscontaining impurities characterized by a broad (wide)melting point range (higher than 2) °C

Melting point used to:

1. Determination the purity criteria

Ex. M.P. of impure Benzoic acid = 121 – 124 °C

2. Identification of the compounds

Ex. M.P. of pure Benzoic acid = 121 – 122 °C

Melting Point

Broad Sharp

Difference More than 2 degrees

Difference Less than 2 degrees

Single and pure compound

Presence of impurities, or existence of more than one compound

• Impurities lower melting point:

– takes less energy to disrupt crystal lattice when impurities are present

– melting point will be lower

– melting point will be broader

Melting point apparatus

Classical melting

point apparatus

Digital melting point

apparatus.

Apparatuses used in determination of Melting point

Stand and Clamp

Beaker

Heating Source

Test tube

Capillary tube

Thermometer

Tripod and Wire Gauze (If Bensen Burner used)

Classical (Manual) melting point apparatus

When the first solid particle starts turning

to liquid record the temperature till al the

solid has been converted into liquid.

This is the melting range

Type of baths for classical melting point apparatus:-

1- Water bath (used for heating less than 100 oC)

2- Oil bath (used for heating 100 – 160 oC)

3- Acidic bath (used for heating 160 – 310 oC)

4- Silicon bath (or wax) more than 300 oC

Beaker

Heater

(any other

heating source)

One of the following

SAMPLE SIZE

First transformation from solid is 72 oC

Last particle which transferred from solid to liquid is at 73 oC

Pure Ibuprofen extracted

from commercial drug

Commercial Ibuprofen

drug (not purified)

First transformation from solid is 74 oC

Last particle which transferred from solid to liquid is at 77 oC

Exp. 1Melting point :( mp)1- Close one end of a standard melting –point tube in a Benzene flame.

2-Inroduce the sample to a depth of about 2mm at the sealed end of the tube.

3-place the tube in an electrically heated melting-point apparatus.

4- Adjust the rate of heating so that the temperature rises about 3-4 for a min.5-Watch the temperature carefully .Note it down in your report; deliver it with answers of questions to your supervisor